For those that need to add external DACs on rockpi-s with the new kernel radxa image.
- Download the dts file from https://raw.githubusercontent.com/eragefe/Rockpi-S/master/rockpis_i2s_newradxaimage.dts
- Copy it to /boot/dtbo
- Start rsetup and navigate to overlays(confirm with yes) > install 3rd party overlay navigate to and choose rockpis_i2s_newradxaimage.dts
- Reboot
It should be all